Variable volume hydraulic pump



ug. 29, 1961 P. G. STEWART VARIABLE VOLUME HYDRAULIC PUMP 3 Sheets-Sheet1 Filed Aug. 18, 1958 INVENToR. PHA/1p 6. Srewner ,a L M, 7&4@ 774ML@ iATTORNEYS' l e LU i L Aug. 29, 1961 P. G. STEWART u U S H Py B faam/12:'WM

A Trag/fyi Aug 29, 1961 P. G. STEWART 2,997,956

VARIABLE VOLUME HYDRAULIC PUMP Filed Aug. 18, 1958 s sheets-sheet s INVEN TGR. 10H/UP 57E-wmf MEMS/aw A rroe/VEYJ Patented Aug. 29, 19612,997,956 VARIABLE VDLUW HYDRAULIC PUMP Phillip G. Stewart, Oak Park,Mich., assigner to Dynex, Inc., Pewaukee, Wis., a corporation ofDelaware Filed Aug. 18, 1958, Ser. No. 755,659 8 Claims. (Cl. 103-41)This invention relates to hydraulic pumps of the type having multiplepumping plungers which are alternately reciprocated by an eccentricwobble plate. The invention iinds particular utility in a pump of thistype which has the pistons in axial parallelism and in which the wobbleplate is rotated. More particularly, the invention pertains to such apump having by-pass means for the pumping units by which the volume ofthe pump may be readily varied.

Prior art pumps of this general type have been proposed wherein theby-pass iluid is used primarily to lubricate the moving parts of thepump. These have been rather complicated arrangements utilizing slidingsleeves actuated by shiftable spiders and have presented leakageproblems resulting in an inefficient pump.

In accordance with the present invention, -a multiple piston hydraulicpump has been provided which has an improved adjustment means foractuating by-pass valves and thereby readily varying the volumetricoutput of the pump. The invention further provides that this 'by-passmeans may function as an auxiliary inlet when not `functioning toby-pass iluid, thereby contributing to an increase in pump eciency.

The invention further contemplates novel adjusting means by which the`amount of uid diverted by the by-pass means can be readily controlled.The arrangement is such that the fluid can be by-passed at a nominalpressure for any delivery rate.

The by-pass means and its adjustment are so timed in their functioningso as not to interfere with the positive opening of the inlet checkvalves in the pistons and at the proper time during their operatingcycle.

The adjustable controlling means for the by-pass valves comprises aneccentric member carried by an axially shiftable shaft, the phase of`said eccentric in respect to the wobble plate being changeable by saidaxial movement of the shaft. The result is a quickly adjustable flowcontrol means.

These and other objects and advantages will appear hereinafter as 4thisdisclosure progresses, reference being had to the accompanying drawingsin which:

FIGURE 1 is an axial cross-sectional view of a pump embodying theinvention;

FIGURE 2 is an end View of the pump of FIGURE l, certain parts brokenaway and in section for clarity of the drawings;

FIGURE 3 is an enlarged fragmentary view, in section, of one of theby-pass check valves;

FIGURE 4 is a side View of the adjusting cam as shown in FIGURE 1, buton an enlarged scale;

FIGURE 5 is an end view of the adjusting om shown in FIGURE 4;

FIGURE 6 is a perspective view of the cam member shown in FIGURES 4 and5;

FIGURE 7 is a layout of the cam showing various pumping capacities ofthe pump;

FIGURE 8 is a projection from FIG. 7 and showing the path of the by-passvalve travel when the pump is operating at one-quarter stroke;

FIGURES 9-13 are cross-sectional views of the cam, taken on lines 9 9 to13--13, respectively, in FIGURE 1, but on an enlarged scale, andshowing, respectively, the paths travelled by the by-pass check valvewhen the pump is operating at full, three-fourths, one-half, one-fourthand zero strokes.

FIGURE 14 is a fragmentary axial cross-sectional View of a pumputilizing a modified form of the invention; and

FIGURE 15 is a transverse cross-sectional view taken on line 15-15 ofFIGURE 14.

Referring in greater detail to the drawings, and particularly to FIGURE1, the pump housing includes a drive housing 15 having a cylinder barrelhousing 16 secured thereto by cap bolts 17 with an oil ring seal 18therebetween. Fluid is furnished to the pump intake chamber 19 throughthe inlet opening 20. A common annular discharge passage 21 is formed inthe cylinder housing 16 through which pressure iluid is discharged intothe `main outlet port 22. isolating plugs 23 are removable, if desired,and a portion of the pressure fluid may be diverted to separate sourcesof utilization through conduits (not shown) insertable in place of anyof the isolating plugs. For a more complete description of these plugsand their functions, reference may be had, if desired, to the co-pendingU.S. application of David T. Blair, Serial Number 661,334, tiled May 24,1957, issued on June 21, 1960, as Patent No 2,941,475, and entitledHydraulic Pump, said application being assigned to the yassignee of thepresent application.

A drive shaft 25 is mounted on anti-friction bearings 26 in the bore 27of the drive 'housing and has a conventional shaft seal 28 thereon. Awobble plate 30 is iixed to shaft 25 by key 31 and carries a thrustabsorbing bearing plate 32 on the anti-friction bearing assembly 33.Another thrust bearing assembly 34 is mounted behind the swash plate 39.The inner end of the drive shaft is piloted on the anti-frictionbearings 35 which are mounted in the bore 36 of the cylinder housing.The inner end of the drive shaft has a bore 37 therein for purposes thatwill appear hereinafter.

The cylinder housing has a plurality of circumferentially spaced bores39 in each of which is iiXed the cylinder cartridges 48 by means of pins41. A piston 42 is reciprocated Within each of the bores 43 o-f thecartridges to eiiect suction and discharge strokes. A pumping stroke (tothe right as viewed in FIGURE l) is delivered to the piston by therotating eccentric surface 44 of the swash plate assembly. A spring 45urges the piston to the left and against the surface 44 as the suctionramp of the swash plate 32 passes by.

For a more complete description of the cylinder cartridges 40, thepiston inlet check valves 46 and their spacers 47, reference may be hadif deemed necessary, to the co-pending U.S. application of William R.Leisner, Serial Number 685,441, filed September 23, 1957, issued onl'uly 19, 1960, as Patent No. 2,945,444, and entitled, Hydraulic Pump,which has also been assigned to the assignee of the present application.It is believed sufiicient to say, however, for purposes of thisdisclosure, that fluid is supplied to the pumping chamber 48 through thebores 49 extending through the piston, past ball check 46 and throughspacer 47. Thus the inlet chamber 19 and bores 49 form an inletpassageway for supply Huid. The ball 46 is unseated when the pistonbegins its suction stroke (left as viewed in FIGURE 1) and it isdesirable to have the ball 46 unseat before fluid is admitted to thepumping chambers via other inlets as will later become more apparent. Itis important for eficient operation of the pump that a steady andturbulentfree ow of fluid passes into the pumping chamber. Pressurefluid is discharged during the pumping stroke of the piston through theoutlet check valves 5i) and into the discharge chamber 21.

The cylinder housing 16 also has a chamber 52 which is in uidcommuication with the inlet chamber via cross bores 53. A cam member 55is mounted in the bore 37 of the drive shaft and extends into thechamber 52. 'Ihe member 55 is fastened by key 56 to the drive shaft 25for rotation therewith but is axially movable the respect to thedriveshaft Within the bore 37. A spring 58 surrounds part of member 55and urges the latter to the right as viewed in FIGURE l. A cross bore 59and connecting bore 60 place chamber 52 in fluid communication with thebottom end of bore 37 to prevent any build-up of pressure therein whichwould cause malfunction of the control means to be described.

The cam member 55 also includes an enlarged cam i portion comprising amajor diameter 63 and a minor diameter 64 which are connected by theinclined portion 65 extending in spiral fashion around the cam. Theshape between the various cam surfaces 63, 64 and 65 Valong an axialline on the cam periphery are in the nature of simple harmonics, and theangle b of the inclined surface 65, as shown in FIGURE 4 for purposes ofillustration, is 30 degrees with respect to the cam axis. Thisparticular angle has been found satisfactory for smooth operation of thecam and the valves actuated thereby, but should not be interpreted aslimiting the invention to any particular angle of this inclined surface.It does, however, provide a gradual transition of direction of movementfor the cam follower to be described.

The cam member can be shifted in an axial direction to any one of aplurality of positions in order to vary the amount of uid which isby-passed by means to be presently described. By so adjusting the axialposition of the cam, the pumping pistons discharge pressure Huid to theoutlet chamber 21 through only a predeterminable portion of theirstroke.

This axial adjustment of the cam is shown as being by a manuallyoperated knob 67 which extends from the end of the pump, althoughsuitable automatic actuating devices, particularly of the hydraulicallyoperated type, may be employed for this purpose. A large nut 68 Vislixed by pin 69 within the large counterbore 70 in the end of thehousing. The nut threadably engages the shaft 71 which is piloted inanti-friction bearing assembly 72 in the cam member. 'Ihe shaft 71 isfastened to knob 67 by the key 73 which causes the shaft to rotate withthe knob, but permits axial shifting therebetween. A snap ring 74rotatably holds the knob in the bore 70. Thus as the knob is Yturned ineither direction, the cam member is shifted axially in a correspondingdirection to either cause more uid to be by-passed back to the inletsupply or discharged as follows.

Y A by-pass check valve assembly 75, shown in enlarged detail in FIGURE3, is mounted in the housing 416 between each of the pumping chambers 48and the central chamber 52, the latter communicating with the inletchamber 19 via passages 53. More particularly, annular groove 76 aroundthe periphery of cylinder cartridges 40 together with their connectingcross bores 77 place the by-pass valve bore 78 in lluid communicationwith thefpumping chambers 48.

' receive a tool for inserting and removing the assembly.

A valve element 83 is slidable in the plug 81 and has Ya tapered surfaceS4 which sealingly engages a complerntary tapered bore in the plug.Circumferentially spaced guides 85 of the element 83 keep the lattercentered the bore of the plug and insure proper seating of the valveelement. A hardened ball 86 is carried in the inner end of the valveelement and acts as a cam follower in following the contour of the cam.

When the ball 86 is on the major diameter 63 of the cam, the valvesurface 84 is held off its seat to permit lluid to by-pass from thepumping chambers V4S to the inlet vchamber 19. When the ball `is on theminor Vdiameter, the spring 88 holds the valve Yelement seated Y insealing engagement with the plug Y81 in which 'case `all ofthe pressurefluid being pumped by the pistons is A valve seat plug 81 is thread- Y 4delivered to the discharge passage 21. In moving from one diameter ofthe cam to the other, the ball rides on the inclined surface 65, yandits transition is in a harmonic motion as shown in FIGURE 8.

FIGURES 9 to Y13 are Ycross-sectional viewsV of the cam taken on lines9-9 to 13s-13, respectively, in FIGURE 1. FIGURE 9 represents thatportion of the cam which results in, a full discharge stroke of thepiston, that is, the piston discharges its entire pumping capacityduring the full 180V degrees rotation of the wobble plate, and duringwhich no pressure fluid is by-passe via valve assemblies 75.

It will be noted that in each of FIGURES 9-13, a lag of about l5degrees, indicated by the letter a,'is provided after piston leaves thetop dead center position. The curvilinear arrows of FIGURES 9-13indicate the direction of rotation of the cam. 'I'his lag insures thatthe by-pass valves are held shut and are ineffective to act as auxiliaryinlets for the pumping chambers until after the piston inlet valves 46have been Vopened fully at the beginning of the suction stroke of thepistons. This synchronization of the by-pass and piston inlet valves isinsured by the fact that the wobble plate and the cam member are bothfixed to the driveshaft for rotation as a unit. As a result, they cannotget out of phase with one another.- The portion of the cam to the leftof the vertical centerline in FIGURES 9-13 represents the suctionportion of the cam Which corresponds to the suction ramp of the wobbleplate.

The dotted lines O and C in FIGURES 9-13 represent the opening andclosing positions of the by-pass valves.V

Thus FIGURE l() represents the cam position where the piston isdischarging its pressure fluid to the discharge passage 21 forthree-fourths of its discharge stroke.Y FG- URES ll, l2 and 13 similarlyrepresent one-half,one quarter, and zero pumping strokes of the pistons.In any of the positions where the by-pass valve is open during thedischarge stroke, as in FIGURES l0-13, it will be noted that the by-passvalve is open under action of the cam-'at the beginning of the dischargestroke. As a result, any by-passing of fluid that takes place occurs atnominal pressure, that is, before pressure builds up in the chambers 48.

The by-pass Valves 75 also act as auxiliary uid inlets for the pumpingchambers 48. As previously mentioned, however, this auxiliary inletfeature does not come into operation until after the piston inlet valves46 are fully open and admitting uid themselves. After the 15 degree laga has elapsed in the initial portion of the pistons suction stroke, thecam surface 65 of the eccentric member 55 causes the ball 86 to ride upto the major diameter Y 63, thus opening the by-pass valves during Ythesuction stroke of the pistons. When operating at full stroke, as shownin FIGURE 9, the cam causes the by-pass valves to close about l5 degreesbefore the discharge stroke commences. In the other FIGURES 10-13, theclosing of the by-pass valves is correspondingly delayed, depending onthe length of the piston stroke through which it is desired to by-passuid.

FIGURE 8 shows a projection from FIGURE 7 for the one-quarter strokeposition of the cam. It Will be seen that the auxiliary inlet operationof the by-pass valves begin 15 degrees after the beginning of the pistonSuction stroke. As the piston changes from a suction to a dischargestroke the by-pass valves remain open until the last one-quarter portionyof the piston discharge stroke.

` Then during the last quarter ofthe discharge stroke, the

Shaft 90 is piloted at its other end 92 in the externally threadedmember 71a. Member 71a is prevented from turning relative to the controlknob 67a, but is axially slidable in respect thereto, by means ofthe key73a. A spiral groove 94 is formed on the periphery of the tubularportion 91, and a ball 95 set in the latter engages this groove. Theball and groove constitute a driving connection between the drive shaft2S and shaft 90.

The shaft 90 also has eccentrically formed portion 96, which forms aneccentric or cam, lupon which is rotatably mounted, on anti-frictionbearings 97, the multifaced collar 98. The various faces 99 of thiscollar are engaged by the shoes 160 of the valve element 84a and thiscollarshoe arrangement provides particularly good contact between theparts and very smooth valve operation.

The operation of this modified form lof the invention is as follows:Turning the control knob 67a causes the member 71a to slide axially,carrying with it the shaft 90. The spring 101 acts to urge the shaft tothe right (FIG. 14) when the knob is turned to allow the shaft to movein that direction.

Axial movement of shaft 90 causes it to rotate by the action of ball 95riding in the spiral groove 94, and this shaft rotation causes the camor eccentric portion 96 of the shaft 90 to change position relative tothe swash plate 44. In other Words, the phase of the eccentric inrelation to the swash plate may be readily varied by the control knob67a so as to vary the point during piston travel at which these by-passvalves 84a will open. The timing of the eccentric relative to thebeginning of the suction stroke of the pistons 42 may be such as topermit these valves 84a to remain open a short time after commencementof the suction stroke, and thereby function as auxiliary inlets.

Both of the modications shown, therefore, provide a control means bywhich the opening of the by-pass valves can be readily varied oradjusted in respect to the pumping stroke of the piston and both alsomay act as auxiliary inlets during a part of the piston suction stroke.

By means of this invention a readily adjustable controlling means isprovided for the by-pass valves which is synchronized and properlyphased with the piston driving means. Therefore, the proper and eicientoperation of the regular inlet valves in the pistons is assured when theby-pass valves act as auxiliary inlet valves. By the specific means ofthe ball check valves for by-passiug fluid, leakage problems have beenreduced considerably. Any by-passing of iiuid is done at nominalpressures which in itself results in an eicient pumping mechanism withlittle irictional heat buildup and leakage.

The cam controlling mechanism provided by the present invention actuatesthe by-pass valves with a smooth action which contributes materially toquiet and troublefree pump operation, and a hydraulic pump has beenprovided whose volumetric output is easily adjustable.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:

l. In a hydraulic pump of the type having a plurality of cylindersforming pumping chambers, a piston having valve means thereinreciprocable in each of said cylinders, means contacting said pistons toreciprocate said pistons in suction and discharge strokes, a iiuidsupply inlet chamber in uid communication with said valve means foradmitting fluid through said pistons to said pumping chambers during asuction stroke of their respective piston, an outlet port in fluidcommunication with said pumping chambers through which pressure uid isdischargable during a. piston discharge stroke, the improvement residingin iiuid by-pass means between at least some of said pumping chambersand said inlet chamber for diverting iiuid pumped by said pistons duringan initial portion of their discharge stroke into said inlet chamber,and means connected and synchronized With said piston reciprocatingmeans to actuate said bypass means.

2. A hydraulic pump comprising, a plurality of cylinders forming pumpingchambers, a piston having valve means therein reciprocable in each ofsaid cylinders, a rotary wobble plate to reciprocate said pistons insuction and discharge strokes, a fluid inlet chamber in fluidcommunication with said valve means for admitting uid through saidpistons to said pumping chambers during a suction stroke of theirrespective piston, an outlet port in fluid communication With saidpumping chambers through which pressure iiuid is dischargeable during apiston discharge stroke, a by-pass valve between said pumping chambersand said inlet chamber, for diverting iiuid pumped by said pistons intosaid inlet chamber, and means synchronized with said wobble plate toactuate said by-pass valves.

3. A hydraulic pump comprising, a plurality of cylinders forming pumpingchambers, a piston having valve means therein reciprocable in each ofsaid cylinders, a rotatable wobble plate means to reciprocate saidpistons in suction and discharge strokes, a uid inlet chamber in uidcommunication with said valve means for admitting uid through saidpistons to said pumping chambers during a suction stroke of theirrespective piston, an outlet port in fluid communication with saidpumping chambers through which pressure fluid is dischargeable during apiston discharge stroke, fluid by-pass means between said pumpingchambers and said inlet chamber for diverting fluid pumped by saidpistons into said inlet chamber, and a rotary cam secured to said wobbleplate means for rotation therewith to actuate said by-pass means.

4. A hydraulic pump comprising, a plurality of cylinders forming pumpingchambers, a piston having Valve means therein reciprocable in each ofsaid cylinders, means engageable with said pistons to reciprocate saidpistons in suction and discharge strokes, a iiuid inlet chamber in fluidcommunication with said valve means for admitting fluid through saidpistons to said pumping chambers during a suction stroke of theirrespective piston, an outlet port in fluid communication with saidpumping chambers through which pressure fluid is dischargeable during apiston discharge stroke, a valve between said pumping chambers and saidinlet chamber for diverting iluid pumped by said pistons into said inletchamber, and means synchronized with said piston reciprocating means toopen said valves during a portion of its corresponding pistons dischargestroke and also during said pistons suction stroke.

5. A hydraulic pump comprising, a plurality of cylinders forming pumpingchambers, a piston having valve means therein reciprocable in each ofsaid cylinders, means contacting said pistons to reciprocate saidpistons in suction and discharge strokes, a uid inlet chamber in uidcommunication with said valve means for admitting iluid through saidpistons to said pumping chambers during a suction stroke of theirrespective piston, an outlet port in fluid communication with saidpumping chambers through which pressure fluid is dischargeable during apiston discharge stroke, a valve between said pumping chambers and saidinlet chamber for diverting uid pumped by said pistons into said inletchamber, and a rotary cam secured to 'said piston reciprocating meansfor rotation therewith to open said valves.

6. A hydraulic pump comprising, a plurality of cylinders forming pumpingchambers, a piston having valve means therein reciprocable in each ofsaid cylinders, means engaging said pistons to reciprocate said pistonsin suction and discharge strokes, a uid inlet chamber in iiuidcommunication with said valve means for admitting iiuid through saidpistons to said pumping chambers during a suction stroke of theirrespective piston, an

Youtlet port in uid communication with said pumping chambers throughwhich pressure fluid is dischargeable Vduring a piston discharge stroke,a valve betweengsaid pumping chambers and said inlet chamber fordiverting uid pumped by said pistons into said inlet chamber, a rotarycam secured to said piston reciprocating means for rotation therewith toopen said valves, and adjustable control means for shifting said cam tovary the length of time during the piston :discharge stroke in whichsaid valves are open.

7. A hydraulic pump comprising, a plurality of cylinders forming pumpingchambers, a piston having value means Vtherein reciprocable in each ofsaid cylinders, means contacting said pistons to reciprocate saidpistons in suction and discharge strokes, a fluid inlet chamber in fluidcommunication with said valve means for admitting uid to said pumpingchambers during a suction stroke of their respective piston, an outletport in fluid communication with said pumping chambers through whichpressure uid is dischargeable during a piston discharge stroke, a valvebetween said pumping chambers and said inlet chamber for diverting fluidpumped by said pistons into said inlet chamber, an eccentric membersecured to said piston reciprocating means for rotation therewith toopen said valves, and adjustable control means for rotationally shiftingsaid member in respect to said piston reciprocating means to vary thelength of time during the piston discharge stroke in which said valvesare open.

8. A hydraulic pump comprising, a plurality of cylinders forming pumpingchambers, a piston having valve means therein reciprocable in each ofsaid cylinders, means contacting said pistons to reciprocate saidpistons in suction and discharge strokes, a tluid inlet chamber in fluidcommunication with said valve means for admitting iiuid to said pumpingchambers during a suction stroke of their respective piston, an outletport in uid commeans to permit axial shifting of the former and therebychanging of the rotational phase between said eccentric and said pistonreciprocating means, and means to axially shift said control shaft.

References Cited in the file of this patent UNITED STATES PATENTS709,929 Raven Sept. 30, 1902 718,132 Lamplough Jan. 13, 1903 906,022Hesselman Dec. 8, 1908 1,336,803 Woerner Apr. 13, 1920 1,416,731 MartinMay 23, 1922 1,768,102 Bellem June 24, 1930 1,895,259 Muller Ian. 24,1933 1,909,961 Hofmann May 23, 1933 1,952,154 Atteslander Mar. 27, 19341,990,263 Benedek Feb. 5, 1935 2,006,879 Benedek July 2, 1935 2,093,477Parsons Sept. 21, 1937 2,142,086 Alden Jan. 3, 1939 2,213,994 RankinSept. 10, 1940 2,300,313 Pool Oct. 27, 1942 2,453,402 Bell Nov. 9, 19482,474,396 Groves June 28, 1949 2,664,048 Huber Dec. 29, 1953 FOREIGNPATENTS 496,546 France Apr. 3, 1918

